Blower fan and AC Clutch are both fairly high amp consumers. Both are likely to cause overheating at the fuse or connectors. You might the running new wire, heavier than factory around the suspect plug under the dash.
Alternate: Use the factory wiring to switch a relay to the fan or both fan and AC Clutch. Heavy wire (10ga) from 12V+ source, to new inline fuse, to the load side of relay, then on to the fan or clutch.
MB had a similar problem on W126 cars. In that case, the fuse generated heat and melted surrounding plastic. The factory solution was to pick up a 12v bus under the fuse panel, run a 10 ga wire (metric similar size) out to the inner fender where a one fuse box held a 25 amp fuse in place of the original 20 amp, then on to the fan.
as far as I can tell non of the hvac has any connection to the can bus wires, or shared power/ grounds with the abs, air bag or cluster modules. The ecu has independant wiring that signals the cooling fan to activate and compressor clutch to enguage. I'd like to think the correlation between running the ac/ high outdoor temps is coincidence, but i won't rule it out. It's an issue that's been on and off since it got hot out, and has happened without the ac on, but I've never been able to get home and get the laptop on it and start eliminating modules to see what changes.
I had thought of low voltage issues causing the issue, all the fuses, wiring are in good shape, short run to the fan controller too, and independent of the ecu and other models power and ground supply. The "battery" power distribution/fuse box is noted for getting overheated, however it's pretty new with heavier wiring coming from the alternator and new fuse strips.
Vcds faults seem to point to one of the 3 models taking a poop, or a wiring issue, not low voltage issues. Additionally, I don't have any faults on the engine can bus (different bus then the other modules use.)
If I have time when I have off I'll have to take the dash completely out to get at the "splice" where the 3 modules all connect before going to the cluster. The can bus wires exit the cluster then go to the ecu. It's a stupid set up, and there's a possibility all the issues are being caused by the cluster, which is its own can of worms if it needs replaced.
I did rule out all associated under hood wiring from the ecm to the fire wall connector. Cleaned up a bunch of unused wires from whoever did the manual swap, and removed all the power wires and can bus wires from the tcm, which removed several potential issues/failure points.
I appreciate anymore thoughts or ideas, being how infrequently it actually acts up I'm pretty stumped at this point, with less but more invasive things to check out.
So far the only good thing that's come from all this mess, is I'm pretty sure I figured out why the cruise control doesn't work. One of the clutch pedal switches isn't activating correctly, so the car thinks the clutch is pushed in all the time. (Yep, stupid design there too, 2 different switches, one for the starter and one for the cruise control)
when it did
